The invention relates to cartridges for receiving pasty materials. The use of cartridges is customary today in very many product groups. In addition to single-component and multi-component adhesive and sealing substances as well as printing inks, dental molding masses are also offered in plastic and aluminum cartridges. Many of these products are damaged on storage in the cartridge or have only short service lifetime due to air bubbles that are introduced, or diffusion through the packaging material.
The air bubbles arise in the cartridge when the piston is inserted into the cartridge opening after filling. Since the pistons must have a function of sealing to the cartridge wall, the air cushion located between the product and piston is at least partially enclosed. In the case of moisture-sensitive products, hardening can occur at the edges of incursions of air.
In the case of products containing filling substances it is a known problem that, at pastes' boundary surfaces with the air, settling of liquid components occur that can interfere with the use of these pastes.
In particular, in the case of multi-component products for automatic mixing systems with static or dynamic mixers, air bubbles lead, in most double cartridges, to varying mixture ratios since the air bubbles under the feed pressure increasing at the beginning are first compressed and delay the application of the product. This then leads at the end, with subsiding feed pressure, to re-squeezing of the bubble-containing component. Particularly in the case of pastes fed by hand through lever function, a constantly varying mixing ratio results thereby. However, this interference also occurs in all the other hand-driven, pressure-driven, or motor-driven manual or floor-mounted devices.
An additional problem for several products is the leakage of constituents or the penetration of moisture or other components of the air.
While in cartridge bodies, sufficient barrier properties can be achieved by the use of, for example, aluminum or increased wall thicknesses in plastics, the plastic pistons frequently form the weakest point of the cartridge.
There have been many attempts to provide cartridges having good barrier properties and de-aeration at the same time.
DE 100 29 799 A1 relates to a cartridge piston in which the piston shoulder pressed due to the conveyance pressure of the application unit onto a spreading ring pointed into the piston in such a manner that it seals at the wall of the cartridge. DE 42 29 588 A1 describes a cartridge piston with elastic piston base and a final protuberance whose outer diameter is greater than the inner diameter of the cartridge. In EP 0 301 327 B1 (DE 8710233 U1) a cartridge piston is described in which the piston shoulder presses on the wall of the cartridge in such a manner that a seal is formed by a reinforcing ring that can be pushed in so that it clamps on a spreading ring pointed into the piston. DE 34 05 547 (EP 0 152 373) discloses a piston with an annular groove running obliquely to the wall of the cartridge into which an elastic sealing ring is admitted. DE 34 35 576 deals with a follower piston for dispensers with a de-aeration opening that can be sealed. DE 36 35 849 A1 describes a piston that can be de-aerated for dispensers with a pointed connecting piece. In WO 90/05096 a de-aeratable piston with self-securing stoppers is presented. DE 23 02 364 A1 has as its object a de-aeratable piston for cartridges with a pointed sealing stopper contained in the de-aeration channel sitting in the middle. EP 1 209 098 A1 relates to a cartridge with pistons for the processing of tubular bags in customary application pistols. In EP 281 755 B1 (U.S. Pat. No. 4 ,834,268) the piston has an annular groove into which an elastic sealing ring is admitted. EP 344 491 B1 describes cartridges with a piston that has a sealing ring and radial de-aeration channels leading to a de-aeration hole to be sealed by means of a screw. EP 463 991 B1 relates to cartridges with a piston that have a sealing ring and radial de-aeration channels leading to a de-aeration hole with stoppers. EP 497 739 B1 (similar to U.S. Pat. No. 5,400,926) recommends cartridges with a piston that has a sealing ring and radial de-aeration channels leading to a de-aeration hole with stoppers where, in front of the sealing ring, sealing lips are still disposed whose encircling groove empties into the de-aeration channels. In DE 196 43 506 A1, the piston of an application unit is structured as two parts for the pressure load after the conveyance. DE 197 14 331 A1 describes a cartridge piston that has channels or grooves running in the radial direction between a central de-aeration hole and the edge of the piston.
In each of EP 344 491, EP 463 991, EP 497 739, U.S. Pat. No. 5,400,926, DE 197 14 331, and WO 90/05096 pistons for cartridges or dispensers are mentioned, each of which ensures the de-aeration by a channel contained in the center of the piston. The channel is then sealed in an additional second step with a separate part 1 in the form of screws or stoppers. Thereby, the length of the cycle in filling is clearly increased.
This disadvantage of the increased expenditure in filling can be eliminated, as described in DE 23 02 364 A1 and DE 36 35 849 A1, by the necessary stoppers already being a part of the piston and only having to seal the de-aeration channel by pressing in after the aeration.
Another way is described in DE 100 29 799 A1 by, on the base of the piston, the sealing edge facing the product being so small that the air can escape during insertion of the piston. In order to have the necessary sealing action during application of the product under high pressure, the piston contains in its interior a spreading ring that causes an extension of the base of the piston up to the wall of the cartridge due to the pressure of the applicator piston.
In EP 301 327 A2, the principle of the spreading ring is used, but the extension is not only caused by the applicator but rather, in a second processing step, a reinforcing ring is pushed in there in such a manner that it clamps onto the spreading ring, which provides for an immediate and long-lasting extension of the base of the piston.
A piston with an elastic base whose rear edge abuts the edge of the cartridge due to its greater diameter is mentioned in DE 42 29 588 A1.
The realizations of the state of the art still leave something to be desired with regard to de-aerability, barrier properties, and the simplicity of processing and filling.
It is thus the objective of the invention to provide cartridges that can be processed during filling without incursions of air, permit as simple and quick a filling as possible, offer good barrier properties against moisture, and have high mechanical strength in order not to deform under conveyance pressure.
By a special development of the piston and, in given cases, a special combination of various materials being used, all these required properties can be implemented and can be adapted to specific requirements.